The present invention relates to the construction of high Q passive devices, typically used for example in radio frequency applications. Such devices are notoriously difficult to incorporate in the semiconductor die because of various factors: The quality factor (Q) of both lumped and distributed reactive components is primarily determined by the resistance of the metal, dielectric losses and parasitic reactances. The actual inductive and capacitive values in lumped components is greatly limited by the available area on the semiconductor die. Similarly, distributed transmission line resonators are difficult to configure on a semiconductor die for desired frequencies also because of space limitations. The usual practice is to place the lumped reactances on the PC board. However, the parasitic reactances associated with conventional package technologies often seriously degrade the performance of a functional circuit. For example, in power amplifier applications, the parasitic reactance of the package leads often approaches or exceeds the output impedance of the active semiconductor device. In many cases, the package reactance negates the possibility of building acceptable power amplifiers on silicon or silicon-germanium processes. Similar arguments can be cited for small signal applications as well.
Integrated circuits are typically mounted in plastic or ceramic packages that connect the semiconductor die to leads or balls which are subsequently soldered to a PCB. Some package types contain multiple metal layers, e.g. a flip-chip ball-grid array, in order to route the I/O pads and utility pads to the external contacts of the package.
FIG. 11, for example, shows a typical ball-grid package. A semiconductor die 1102 is mounted to a substrate 1112 is secured thereto by an underfill epoxy compound 1106. The substrate includes a set of metal interconnect layers to provide an electrical pathway between the solder balls (or "bumps") 1104 of the die and the solder balls 1114 of the substrate. An overmold epoxy 1110 is used to encapsulate the die, thus completing the ball-grid package. FIG. 12 is an enlarged view of a portion of substrate 1112, identified in FIG. 11. It can be seen that the substrate consists of a laminated structure of alternating layers of metal 1212. These metal layers are insulated from each other by layers of insulating material 1210 such as epoxy or ceramic. These metal layers provide interconnections among or between the bonding pads or "bumps" on the semiconductor die 1102. The metal layers are patterned with interconnects (not shown) and vias 1202 which provide interconnectivity among the metal layers.
What is needed is a scheme for providing high Q components in IC devices without having to use discrete components. It is desirable to incorporate such devices within the IC device itself, and thus save space on the PCB while at the same time gaining the advantages made possible by the use of high Q components.